Electrical utilities face the problem of satisfying consumer demand for electrical energy during peak and off-peak demand periods. Total electrical energy demand varies significantly between the peak and off-peak demand periods. For example, energy demand typically peaks on a hot summer afternoon as a result of the widespread simultaneous operation of air conditioning systems, and energy demand subsequently drops during the off-peak period of the late evening. To accommodate very high peak demands, utilities face the options of investing in additional power generating capacity, buying power from other utilities having excess capacity, or using an electrical load management system to control the amount of electrical energy distributed over the electrical distribution network during peak energy demand periods by electrical load reductions, commonly referred to as lead shedding.
Electrical load management systems for allowing an electrical utility to control the load on the electrical distribution network are known in the art. These systems operate to divert energy requirements to minimize electrical black-outs or "brown-outs."U.S. Pat. No. 4,190,800 to Kelly, Jr. et at., entitled "Electrical Load Management System," assigned to the same assignee as the present invention, describes an electrical load management system wherein a utility command center monitors the use of electrical power and, when peak demand periods occur, transmits coded information by radio from the command center to remote receivers mounted at distribution transformers located proximate to the electrical loads. In this patent, the transmitted signal includes address and command data that are decoded at the receivers. Receivers addressed by the command center pass command information over the distribution lines to the electrical loads, and thereby control the operation of the customers' power consuming devices.
Other load management systems utilize separate radio receivers at each customer's location, rather than providing a receiver at the distribution transformer as in the aforementioned patent. Examples of this type system include the types DCU-1120, -1170, -1180, -1190, and -S2000A utility radio switches, otherwise described as digital control units or load control switches, manufactured by Scientific-Atlanta, Inc., Atlanta, Ga., and the type REMS-100 radio switch previously manufactured by General Electric, King of Prussia, Pa. These utility radio switches incorporate an FM receiver that can receive a transmitted signal up to about 25 miles from a transmitter site located at a command center. The transmitter issues commands to temporarily remove power from a selected load. This self-contained receiver is typically mounted on or immediately adjacent to the electrical loads under control, and receives its power from the line that feeds the controlled loads. Switches, jumpers, or other means contained within the receiver configure the receiver to respond only to a particular address or set of addresses, so that different geographical areas, types of appliances, or numbers of consumers may be separately controlled.
Although a utility benefits by implementing load reductions during peak demand periods, such energy management devices typically do not address the impact of interrupted or reduced energy service upon the consumer. A consumer may find the temporary interruption of energy to its air conditioning or forced heating systems to be undesirable if such service interruptions cause abrupt changes in the environmental temperature, such as overheating or underheating. Utilities recognize that consumers' discomfort resulting from energy management control could lead to those consumers seeking the removal of energy management devices from their premises. Because a utility commonly offers an incentive to a consumer in exchange for permission to install an energy control device, the consumer's decision to remove the installed device eliminates the utility's opportunity to control the consumer's energy consumption and wastes the utility's resources.
Prior art energy control systems have addressed the issue of maintaining consumer comfort during energy reduction operations. U.S. Pat. No. 4,819,180 to Hedman et al. describes an energy demand control system for measuring total power consumption of each user and thereafter modifying the user's total power consumption in response to a utility control signal from a remote location. The average total power consumption is modified by an amount correlated with the user's energy usage pattern. If the utility control signal defines a particular percentage for reduction of power consumption by each user, the actual percentage reduction implemented by the demand consumption system is a percentage of the average total power consumption of each user. The demand control system controls the maximum usage of energy for a group of controllable loads located at a consumer's premise. Accordingly, the actual percentage reduction implemented by the system is based upon the total usage of energy by all of the loads at that location and not a specific single load, such as an air conditioner.
The power reduction for a particular user can be interrupted by the Hedman et al. demand control system in the event that the temperature at the user's locale is below a predetermined level. A temperature sensor monitors the temperature in the consumer's building and enables a logic circuit to override the utility control operation should the temperature rise above or fall below predetermined limits. If the logic circuit operates to override utility control operation, the system subsequently releases control of all such loads at the consumer's premises. This interruption of the utility's control operation affects all loads at the consumer's site, including those loads that do not operate to condition the space temperature within the consumer's closed environment.
Although the Hedman et al. demand control system may be effective in reducing the peak energy consumption of individual users in response to a utility's command, the system also suffers from the disadvantage of restoring energy when a certain temperature within the closed environment is measured to both a space conditioning load and a group of loads that do not condition the space temperature of the closed environment. In addition, if a large number of demand control systems are controlled simultaneously by the utility, a significant immediate change in peak energy demand may occur which causes an undesirable spike in the utility energy distribution network.
Another prior art energy management system is described in U.S. Pat. No. 4,341,345 to Hammer et al. This patent describes the control of power consumption of individual space conditioning loads by a programmable temperature control device, such as a thermostat. A radio receiver receives a command signal from the utility company and, in response, the setpoint function of the thermostat is remotely controlled by the utility. Consumer control is removed in response to the utility's command signal. In the cooling mode, the control temperature setpoint is raised to a maximum predetermined temperature limit during peak power consumption periods to reduce energy consumption. Thereafter, the control temperature setpoint is returned to the original temperature set by the consumer and consumer control is restored. Physical discomfort for the consumer is minimized by gradually ramping the control temperature setpoint to the maximum temperature limit during the peak power period.
Although the Hammer et al. system allows the utility to remotely control the temperature setpoint without the consumer's knowledge of setpoint modification, this operation affects space conditioning operations without regard to the consumer's personal comfort level. As a result, some consumers will be more severely impacted by an energy control operation implemented by the Hammer et al. system than others.
To promote energy conservation and to achieve environmental objectives, there is a need for an improved load control device that permits consumers to conserve energy on a continuous basis while affording utilities the opportunity to control peak energy demand. It would be highly advantageous to implement a load management system for controlling the electrical energy supplied to an individual space conditioning load by combining the environmental control and temperature sensing functions offered by a conventional programmable thermostat with the known load control switching function supplied by a load control switch. The system controls distribution of electrical energy to a space conditioning load in response to a utility command and overrides utility control of the space conditioning load upon measuring certain space temperatures within a closed environment. This system also achieves required load reductions from a controllable space conditioning load with a minimum impact on the comfort levels for the occupant of the conditioned location. The utility controls a space conditioning load at each consumer's location to implement a peak energy demand management program.
The present invention provides a novel combination of thermostat and load control switching functions to minimize the costs associated with the manufacture, installation, and maintenance of the discrete components supplying those separate functions. By the use of programmable temperature setpoints for an electronic programmable thermostat, the consumer can conserve valuable natural energy resources while the utility achieves the desired flexibility of peak demand energy control by equitable control operations performed by the load control switch. In addition, a utility can offer the consumer the use of the electronic programmable thermostat as an incentive to join the peak energy demand management program. Simple and economical installation of the system is achieved by combining the desired functions within the same enclosure and powering the system with the same low voltage power source.